Re: Effect of transfer of copyright on free software licenses?

Providing rebate is an obligation on the seller's side in that contract

If you're so hung up on the simultaneity, imagine a case
where a business advertises that any customer who purchased
more than $100 of merchandise in the previous year may come
in to the store and get a free toy penguin.
Oddly enough, the store does not promote this as a unilateral
contract, but as a "reward for our loyal customers".